Now can you imagine what will happen if you spend most of your time in the gym working out on these TesteroneXL smaller type muscle fibers? Do you really expect to grow big when you are doing this? I am not saying that these smaller muscle fibers cannot increase in size, on the contrary, you can make, it is just that you need to train them a little differently. Your calves and forearms muscles are such examples.Many a times, when people's workout methods are wrong and their muscles don't grow, they pin it down on genetics. Have you ever heard people exclaiming, "Oh, my muscles are not growing poor genes." Then they whine and whine about how their parents and siblings are also small built. So it is probably the genes.